1. Field of the Invention
The present invention relates to a magnetoresistance effect magnetic head for a high density digital recording and reproducing apparatus, such as a digital tape recorder or a data storage, and to a manufacturing method therefor.
2. Description of Prior Art
In recent years, the recording density realized by magnetic recording has been raised, thus resulting in that a demand for a thin film magnetic head being heightened which is able to advantageously reduce the width of the track, lower the inductance and raise the transfer rate to be adaptable to the raised recording density as compared with the conventional bulk type magnetic head which has been used widely.
Since the thin film magnetic head is, similarly to a semiconductor integrated circuit, manufactured by using a film forming technology, such as evaporation and sputtering, and a photolithography technology, such as a photomechanical process and etching, a multiplicity of thin film magnetic heads can collectively and accurately be manufactured on one wafer. Thus, the thin film magnetic head can satisfactorily be mass-produced. Therefore, the thin film magnetic head is expected to be mainly used as a magnetic head employed in a magnetic recording apparatus, such as a hard disk drive.
In the above-mentioned circumstance, also the thin film magnetic head is required to have improved performance to be adaptable to the further raised recording density. To improve the performance, a magnetic head has been researched and developed which has a structure formed by combining an inductive thin film magnetic head and a magnetoresistance effect magnetic head (hereinafter called as a "MR head") to record an information signal by using the inductive thin film magnetic head and to reproduce an information signal by using the MR head. Moreover, a combined type thin film magnetic head, having a structure arranged such that the inductive thin film magnetic head and the MR head are formed on one substrate thereof, has been put into practical use.
The MR head is a magnetic head using the magnetic resistance effect of a magnetoresistance effect magnetic device (hereinafter called as an "MR device") to reproduce a recorded signal. The MR head is different from a usual magnetic induction type magnetic head, that is, a magnetic head having a structure in which a wire is wound around a magnetic core, in that the output reproduced from the MR head does not depend upon the relative speed from a recording medium. Namely, the MR head is able to obtain a satisfactorily large output even from a relatively low speed system. Therefore, the MR head is considered to be an essential device for realizing higher density recording and reproducing.
The MR head is mainly classified into a non-shield MR head structured such that the two side surfaces of the MR device are held by non-magnetic members; a shield MR head structured such that the two side surfaces of the MR device are shielded by soft magnetic members for the purpose of improving the reproduction frequency characteristic of the non-shield MR head; and a yoke type MR head structured such that magnetic flux from a recording medium is introduced into the MR device and the MR device is formed into a non-exposed type structure in order to stabilize various characteristics, such as wear resistance. Among the above-mentioned MR heads, the shield MR head has been made most practical. The reason for this is that the shield MR head has a frequency characteristic superior to that of the non-shield MR head and thus excellent resolution can be obtained. Moreover, the shield MR head can easily be manufactured as compared with the yoke type MR head and large reproduction output can be obtained.
The shield MR head is classified into a lateral type head in which a sense current flows in the widthwise direction of the track and a vertical type head in which the sense current flows perpendicular to the widthwise direction of the track. At present, the lateral type shield MR head is mainly used.
The conventional lateral type shield MR head has a structure arranged as shown in FIGS. 1 to 4. FIG. 1 is a plan view showing a circuit pattern of the lateral type shield MR head, and FIG. 2 is a cross sectional view taken along line I-I' shown in FIG. 1. FIG. 3 is a cross sectional view taken along line J-J' shown in FIG. 1. FIG. 4 is a schematic perspective view showing the conventional lateral type shield MR head.
As shown in FIGS. 1 to 4, the lateral type shield MR head is composed of a MR device portion 105 consisting of a first soft magnetic substrate 101, an insulating layer 102 formed on the first soft magnetic substrate 101, a MR device 103 and a biasing conductor 104 formed on the insulating layer 102; a pair of conductors 106 and 107 extending from the two lengthwise directional ends of the MR device portion 105; an insulating layer 108 formed on the MR device portion 105 and the conductors 106 and 107; and a second soft magnetic substrate 110 connected to the upper surface of the insulating layer 108 by an adhesive agent 109.
The biasing conductor 104 is provided for the purpose of applying a bias magnetic field to the MR device 103, the biasing conductor 104 being formed on the MR device 103. The MR device portion 105 formed by laminating the MR device 103 and the biasing conductor 104 is disposed in such a manner that its longitudinal direction runs parallel to a surface M facing a recording medium. Moreover, one of the ends of the MR device portion 105 is ground so as to be exposed to the surface M facing the recording medium.
When an information signal is reproduced from the recording medium by using the above-mentioned MR head, a sense electric current is supplied to the MR device portion 105 through the conductors 106 and 107. As a result, the sense electric current flows in the lengthwise direction of the MR device portion 105 along the surface M facing the recording medium.
In the above-mentioned MR head, it is preferable that each of the conductors 106 and 107 has small electric resistance because the sense electric current is supplied to the MR device portion 105 through the conductors 106 and 107. Since the portions of the conductors 106 and 107 which are connected to the MR device portion 105 are exposed to the surface M facing the recording medium and thus the portions come in contact with the outside air, the portion must have environment resistance.
Accordingly, the conductors 106 and 107 are divided into portions which are exposed to the surface M facing the recording medium and thus brought into contact with the outside air and portions which do not exposed to the surface M facing the recording medium and thus they are not brought into contact with the outside air, the divided portions being made of different materials.
That is, the conductors 106 and 107 are composed of first conductors 106a and 107a extending from two lengthwise directional ends of the MR device portion 105 and second conductors 106b and 107b extending from the rear ends of the first conductors 106a and 107a.
Since the first conductors 106a and 107a are exposed to the surface M facing the recording medium and thus they are brought into contact with the outside air, the first conductors 106a and 107a must have satisfactory environment resistance rather than the electric characteristics. Thus, the first conductors 106a and 107a are made of metal having a high melting point to have satisfactory environment resistance. On the other hand, since the second conductors 106b and 107b are not exposed to the surface M facing the recording medium and thus they are not brought into contact with the outside air, the second conductors 106b and 107b must have satisfactory electric characteristics rather than the environment resistance. Therefore, the second conductors 106b and 107b are made of a conductive material having a small specific resistance.
When the lateral type shield MR head is manufactured, the first step is performed such that the insulating layer 102 is, by sputtering or the like, formed on the first soft magnetic substrate 101. Then, the MR device 103 and the biasing conductor 104, for applying the bias magnetic field to the MR device 103, are formed on the insulating layer 102. Then, the foregoing elements are formed to have predetermined shapes by photolithography so that the MR device portion 105 is formed.
Then, the first conductors 106a and 107a are formed to extend from the two ends of the MR device portion 105 to cover the upper surface of the insulating layer 102, that is, to extend from the two lengthwise directional ends of the MR device portion 105. Then, the second conductors 106b and 107b are laminated on the rear portions of the first conductors 106a and 107a.
As described above, the first conductors 106a and 107a and the second conductors 106b and 107b for supplying the sense electric current to the MR device portion 105 are made such that the first conductors 106a and 107a are made of the material having excellent environment resistance and the second conductors 106b and 107b are made of the material having small specific resistance.
Then, the insulating layer 108 is formed on the overall surface, and then the second soft magnetic substrate 110 are connected to the insulating layer 108 by the adhesive agent 109. The second soft magnetic substrate 110 is connected in such a manner that portions of the rear ends of the second conductors 106b and 107b are exposed to serve as electrodes for establishing the connection with the outside.
After the above-mentioned processes have been completed, a grinding process for grinding the surface M facing the recording medium to expose the MR device portion 105 to the surface M facing the recording medium is performed, and then a terminal forming process is performed such that terminals for establishing the connection with the outside are formed in the electrode portions at the rear ends of the second conductors 106b and 107b. As a result, the above-mentioned lateral type shield MR head can be manufactured.
The frequency characteristics of the lateral type shield MR head having the above-mentioned structure are determined by shield gap distance g between the first soft magnetic substrate 101 and the second soft magnetic substrate 110. The frequency characteristics are improved in inverse proportion to the shield gap distance g. Thus, an information signal having a higher density can be reproduced.
Since the shield MR head has the structure such that the MR device 103, the biasing conductor 104 and the conductors 106 and 107 are held between the first soft magnetic substrate 101 and the second soft magnetic substrate 110, the shield gap distance g is mainly determined by the thicknesses of the MR device 103, the biasing conductor 104 and the conductors 106 and 107. Since the conductors 106 and 107 have the largest thickness in general, the shield gap distance g is determined by the thickness of the conductors 106 and 107.
Therefore, it is preferable for the shield MR head that the thickness of the conductors 106 and 107 be reduced to shorten the shield gap distance g. However, since reduction in the thickness of the conductors 106 and 107 results in the electric resistance of each of the conductors 106 and 107 being enlarged, the load of a sense electric current circuit for controlling the sense electric current which is supplied to the MR device portion 105 is made to be heavier and the impedance is as well as enlarged. As a result, noise level is raised unsatisfactorily. Therefore, the shield MR head having the above-mentioned structure encounters a difficulty in reducing the thickness of the conductors 106 and 107. Thus, the shield gap distance g cannot be made to be a satisfactory value.
To solve the above-mentioned problem, a shield MR head having a structure arranged as shown in FIGS. 5 and 6 has been suggested. FIG. 5 is a plan view showing a pattern of a circuit in the shield MR head, and FIG. 6 is a cross sectional view taken along line K-K' shown in FIG. 5.
The foregoing shield MR head has a structure such that a portion of the insulating layer 108, formed on the overall surface after the first conductors 106a and 107a and the second conductors 106b and 107b have been formed, is etched, the portion being a portion formed on the first conductors 106a and 107a. Thus, the thickness of the insulating layer 108 is reduced in order to prevent projection of the insulating layer 108 over the first conductors 106a and 107a. As a result, the influences of the first conductors 106a and 107a and the second conductors 106b and 107b on the shield gap distance g can be limited. Thus, the shield gap distance g can be reduced. As described above, the shield MR head of the foregoing type is able to reduce the shield gap distance g so that a relatively satisfactory frequency characteristic is obtained.
However, the shield MR head shown in FIGS. 5 and 6 must have a process for etching the portions of the insulating layer 108 on the first conductors 106a and 107a, the insulating layer 108 being formed on the overall surface after the second conductors 106b and 107b have been formed. Thus, there arises a problem in that the number of manufacturing steps cannot be reduced. That is, the above-mentioned shield MR head must have the etching process using the photolithography after the insulating layer 108 has been formed. As a result, the number of manufacturing step is unintentionally increased.